In the PCI 485/2 Serial manual it refers to "User Configerable Bias Resistors". How are they configured?

[tricky]

I am installing a network of two Fieldpoint 1001 units using full duplex wiring to an NI RS485/2 sierial card. The location of the second fieldpoint unit is some 350 feet through a noisy environment. Fieldpoint explorer finds the first fieldpoint unit when wired alone, but when the more remote unit is configred, no modules are found, although the network LED comes on on both units. If the second unit is configured more locally, there is not a problem. Is the problem bias related? In the PCI 485/2 Serial manual it refers to "User Configerable Bias Resistors". How are they configured?

[Ryan_M]

The resistors physically located on the board can be removed/replaced with different resistors in order to achieve the biasing you require. You should be able to desolder and remove the current resistors with easy and replace them with new ones corresponding to your system.

[Aaron_G]

When using RS-485 over long distances, you typically need to add bias resistors to the start point and end point of the RS-485 cable. These bias resistors are nominally 120 Ohms and are installed between the TX+ and TX- wires and the Rx+ and Rx- wires. On a full duplex system, there will be a total of 4, 120 Ohm resistors installed. For your system, 2 are installed at the computer end, 2 at the farthest FP-1001. For diagrams on the installation of the 120 Ohm Resistors, please see pages 2-10 through 2-11 of the FP-1000/1001 User Manual ( http://www.ni.com/pdf/manuals/321631b.pdf ).

When configuring your FieldPoint system, make sure that both FP-1001's have been set to different addresses (pages 2-12 through 2-15 of the above manual) and that you have power-cycled
the modules after you have changed the dip-switch settings.

Regards,
Aaron